1. Field of the Invention
This invention relates to an original reading apparatus of the type in which original image information to be read as a row of information is read by a plurality of imaging systems, and generally to a reading apparatus which is widely usable as a reading system such as facsimile or the like.
2. Description of the Prior Art
An original reading apparatus such as facsimile or the like has heretofore been of the type as shown in FIGS. 1 to 2 of the accompanying drawings. In FIG. 1, reference numeral 1 designates an original, reference numeral 2 denotes a fluorescent lamp for illuminating the original, reference numeral 3 designates a lens, and reference numeral 4 denotes a solid sensor such as CCD. The original 1 is illuminated by the fluorescent lamp 2, the image of the original is formed on the solid sensor 4 by the lens 3 and one line thereof is read, and the original is conveyed in the direction of arrow, whereby the information on the entire original surface is read successively. In such an apparatus, however, the angle of view of the lens 3 has an upper limit and therefore, the distance between the original 1 and the sensor 4 is unavoidably great, and this has led to a disadvantage that the apparatus becomes bulky even if a mirror or the like is used to bend back the optical path. Also, the quantity of light from the marginal portion of the original is reduced relative to the central portion of the original and a uniform output cannot be obtained, and this has led to the necessity of providing for various correcting means. A construction devised as a method for solving these problems is shown in FIG. 2. As shown in FIG. 2, the imaging optical system is constituted by an ommateal optical system comprising a plurality of juxtaposed lenses, and a plurality of solid state image pick-up elements corresponding to the respective lenses are disposed so that each of a plurality of areas into which one direction of the original has been divided is read by each lens and each solid state image pick-up element. The apparatus of FIG. 2 will further be described. In FIG. 2, reference numeral 5 designates an original, and reference numerals 6.sub.1, 6.sub.2 and 6.sub.3 denote parts of image information such as a picture or writing depicted on the original. Reference numerals 7.sub.1, 7.sub.2 and 7.sub.3 designate lenses, and reference numerals 8.sub.1, 8.sub.2 and 8.sub.3 denote the images of the parts 6.sub.1, 6.sub.2 and 6.sub.3, respectively, of the picture or writing on the original. Reference numerals 9.sub.1, 9.sub.2 and 9.sub.3 designate solid sensors, and reference numerals 10.sub.1 -1, 10.sub.1 -2, . . . , 10.sub.1 -n, 10.sub.2 -1, 10.sub.2 -2, . . . , 10.sub.2 -n, 10.sub.3 -1, 10.sub.3 -2, . . . ,10.sub.3 -n denote the photoelectric converting portions of each 1 bit of the solid sensors 9.sub.1, 9.sub.2 and 9.sub.3. The operation of this reading apparatus is as follows. The original 5 is conveyed in a direction perpendicular to the plane of the drawing sheet, and the direction in which a number of lenses 7.sub.1, 7.sub.2, 7.sub.3, . . . and solid sensors 9.sub.1, 9.sub.2, 9.sub.3, . . . are arranged is the main scanning direction. The lenses 7.sub.1, 7.sub.2 and 7.sub.3 cause the reducedscale images 8.sub.1, 8.sub.2 and 8.sub.3 of the parts 6.sub.1, 6.sub.2 and 6.sub.3, respectively, of the picture or writing on the original to be formed on the solid sensors 9.sub.1, 9.sub.2 and 9.sub.3. The images 8.sub.1, 8.sub.2 and 8.sub.3 are inverted images and therefore, even if the outputs of the respective bits of the solid sensors 9.sub.1, 9.sub.2 and 9.sub.3 are arranged in the order of 10.sub.1 -1, 10.sub.1 -2, . . . , 10.sub.1 -n, 10.sub.2 -1, 10.sub.2 -2, . . . , 10.sub.2 -n, 10.sub.3 -1, 10.sub.3 -2, . . . , 10.sub.3 -n from the end, it will not result in the right order of the parts of the picture or writing on the original. Accordingly, it is necessary to take out the outputs of the respective bits, for example, in the order of 10.sub.1 -n . . . , 10.sub.1 -2, 10.sub.2 -1, 10.sub.2 -n, . . . , 10.sub.2 -2, 10.sub.2 -1, 10.sub.3 -n, . . . , 10.sub.3 -2, 10.sub.3 -1. Alternatively, it is necessary to take out the outputs in succession from the end and temporally store them in a memory and then take out them in the right order. Where the head of the recording system is a multihead, the correspondence between each bit of a solid sensor and each bit of a recording head portion corresponding to that solid sensor is taken in reversed relation, whereby signals read by the solid sensor are supplied to the recording system in succession from the end or in parallel and right recording is effected there. That is, each bit of the portion of the recording head which corresponds to the picture or writing 6.sub.1 on the original is just related to each bit of the solid sensor in the same geometrical relation with the portion 6.sub.1 of the original and the image 8.sub.1 thereof. This also holds true of the relation between the solid sensors 9.sub.2, 9.sub.3 and corresponding recording head portions.
The respective solid sensors must read only the image information of a predetermined area of the original, and to avoid reading the information of the other area at the same time, there are provided light-intercepting means 11.sub.1, 11.sub.2, 11.sub.3, 11.sub.4, . . . For example, the light beam from 6.sub.3 which is a part of the image is intercepted by the light-intercepting means 11.sub.2 and accordingly, the photoelectric conversion output of the solid sensor 9.sub.1 becomes a right signal which has read only the part 6.sub.1 of the picture or writing on the original. As regards the length of each solid sensor, in order that reading may be effected at a high resolving power, the length of the photoelectric converting portion row should desirably be equal to the length of each partial image (e.g., 6.sub.1), that is, the lenses 7.sub.1, 7.sub.2, 7.sub.3, . . . should desirably be one-to-one magnification systems, but in the construction of each solid sensor itself, a non-conversion area or light-intercepting means is provided outside of the photoelectric converting portion and therefore, each lens generally is not a one-to-one magnification system but a reduction imaging system. The positional accuracy of the imaging system comprising a plurality of lens systems as shown in FIG. 2 will now be considered. When the imaging lens (e.g., 7.sub.1) has made parallel eccentricity by .DELTA. in the direction perpendicular to the optical axis, if the imaging magnification of the lens is .beta., the amount of movement .delta. of the visual field on the original surface having an imaging relation with a particular solid sensor, in the direction perpendicular to the optical axis, is in the following relation: ##EQU1## where when .beta.&gt;0, the resultant image is an erect image and when .beta.&lt;0, the resultant image is an inverted image.
The fact that the visual field on the original surface having an imaging relation with a particular solid sensor moves in the direction perpendicular to the optical axis leads to a result that the correspondence relation between the images obtained by means of the solid sensors 9.sub.1, 9.sub.2, 9.sub.3, . . . and the original shifts and the finally obtained images suffer from skips or overlaps in the seams between the solid sensors 9.sub.1, 9.sub.2, 9.sub.3, . . . It is therefore desired that the amount of movement .delta. of the visual field on the original surface be made less than a certain predetermined amount determined for the size of 1 bit of the solid sensor.
For example, assuming that the size on the original surface which corresponds to the size of 1 bit of the solid sensor is 83.3.mu..times.1/.beta., in order that the amount of movement .delta. of the visual field on the original surface may be made less than the size on the original surface corresponding to less than 1/4 of 1 bit, namely, 20.8 .mu..times.1/.beta., if the imaging magnification .beta.=-0.8 (inverted reduction imaging of .times.0.8), the amount of movement .delta. must be .delta.=.DELTA.(1+1/0.8).ltoreq.26.0, that is, the amount of parallel eccentricity .DELTA. of the imaging lens (e.g., 7.sub.1) in the direction perpendicular to the optical axis must be 11.55.mu. or less. Likewise, assuming that the size on the original surface which corresponds to the size of 1 bit of the solid sensor is 125.mu..times.1/.beta., in order that the amount of movement .delta. of the visual field on the original surface may be made less than the size on the original surface corresponding to less than 1/4 of 1 bit, namely, 31.25.mu..times.1/.beta., if the imaging magnification is inverted reduction imaging of .times.0.8, the amount of movement .delta. must be .delta.=.DELTA.(1+1/0.8).ltoreq.39.06.mu., that is, the amount of parallel eccentricity .DELTA. of the lens must be 17.4.mu. or less. As will be seen from the foregoing, in order to obtain accurate image information which is free of skips or overlaps in the image of the original relative to the size of the bit at a practical level, the amount of parallel eccentricity .DELTA. of each lens of the plurality of lens systems in the direction perpendicular to the optical axis must be reduced to 10.mu.-20.mu. or less. However, where the imaging lenses 7.sub.1, 7.sub.2, 7.sub.3, . . . are made of a material such as glass which is comparatively stable for temperature and humidity, individual lenses must be separately fabricated and then incorporated, and effecting the position adjustment with respect to the solid sensors 9.sub.1, 9.sub.2, 9.sub.3, . . . at high accuracy of 10.mu.-20.mu. during the incorporation requires much trouble because of the great number of lenses and this forms a factor which impedes mass productivity. Also, if the imaging lenses 7.sub.1, 7.sub.2, 7.sub.3, . . . are molded with a plastic such as acryl and the plural lenses are unitized thereby, the trouble involved in the position adjrustment with respect to the solid sensors 9.sub.1, 9.sub.2, 9.sub.3, . . . during the incorporation will be greatly reduced, whereas a moldable optical plastic such as acryl is greatly variable in dimensions or refractive index for environmental conditions such as temperature and humidity and therefore, it is difficult to reduce the previously shown parallel eccentricity accuracy to 10.mu.-20.mu. or less. For example, as regards the expansion by heat of acryl, its coefficient of thermal linear expansion is .about.6 .times.10.sup.-5 cm/cm/.degree. C. and therefore, assuming that the amount of temperature variation is 40.degree. (e.g., 20.degree. C..+-.20.degree. C.), the amount of linear expansion of acryl having a length of 200 mm is 480 .mu.m. In contrast, the coefficient of thermal linear expansion of silicon (Si) or glass (SiO.sub.2) which provides the substrate for solid sensors is lower by about one unit than that of acryl and therefore, the amount of linear expansion thereof is several +.mu.m under the same conditions as those for acryl, and where ommateal lenses are unitized by the use of acryl, the amount of parallel eccentricity of the lenses with respect to the sensors will be a maximum of several hundred .mu.m and it will be difficult to put acryl into practical use.